The present invention relates to an imaging lens for forming an image on an imaging element such as a CCD sensor and a CMOS sensor. In particular, the present invention relates to an imaging lens suitable for mounting in a relatively small camera such as a cellular phone, a digital still camera, a portable information terminal, a security camera, an onboard camera, and a network camera.
An imaging lens to be mounted in a small camera has been required to have a high resolution lens configuration suitable for a recently developed imaging element with a high resolution, as well as to use a fewer number of lenses. Conventionally, a three-lens imaging lens has been frequently used as such an imaging lens. However, as an imaging element has higher resolution, it is more difficult to obtain sufficient performances only with three lenses. In these years, another lens configuration, a four-lens configuration or a five-lens configuration, has been applied.
Among the configurations, since a configuration with five lenses has a higher design flexibility, it may be expected to apply such lens configuration in a next-generation imaging lens. An imaging lens disclosed in Patent Reference has been known as an imaging lens having such a five-lens configuration.
The imaging lens disclosed in Patent Reference includes a positive first lens having a convex surface on the object side; a second lens having a negative meniscus shape that directs a concave surface on the image side; a third lens having a positive meniscus shape that directs a convex surface on the image side; a negative fourth lens in which both surfaces have an aspheric shape and a surface thereof on the image side near an optical axis is concave; and a positive or negative fifth lens, in which both surfaces are aspheric shape, in this order from the object side.
In this configuration, when a lower limit of Abbe's number of the first lens and upper limits of Abbe's numbers of the second and the fourth lens are respectively assigned, an axial chromatic aberration and chromatic aberration of magnification are corrected, so as to compatible with a high performance imaging lens.
Patent Reference Japanese Patent Application Publication No. 2007-264180
According to the imaging lens disclosed in Patent Reference, it is possible to obtain relatively satisfactory aberrations. Since the total length of the lens system is long, however, it is difficult to attain both miniaturization of an imaging lens and satisfactory aberration correction.
In view of the problems of the conventional techniques described above, an object of the present invention is to provide an imaging lens with a small size capable of properly correcting aberration.